Any work costs money to complete. This money is spent in two parts. One Time Expenditure and Recurring Expenditure. A one-time expenditure is completed when work is done to satisfy a requirement. There are ongoing expenses for the work after it is finished, either monthly or annually.
Example : You can pay developer a one-time fee to create a website. You have to purchase a server to run this website which needs to be renewed periodically.
It is very important to analyze and review many more such expenses beforehand. Everyone allocates money while doing any work. If the cost is not analyzed properly, if the amount of cost becomes more than the allocated money, then it creates a lot of difficulties.